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Travel Time and Congestion

Description: 

Congestion results when the traffic infrastructure lags behind the growth in an area and increases the time it takes to complete a trip by car.  The travel time index and the annual delay per commuter measure the effect of congestion on the amount of time it takes us to travel through the city.  Congestion results in excess fuel consumption and increased costs, both in the expense of the fuel and in the value of the driver's time. Congestion tends to be worse in larger urban areas than smaller ones; however, smaller urban areas may contain pockets of traffic congestion that are just as bad as those found in larger areas.   Increased infrastructure, both in the form of new roads and increased public transportation, can help to alleviate congestion.

Data Source: 

Congestion data were collected from TTI's 2012 Urban Mobility Report (Powered by INRIX Traffic Data) by David Schrank, Bill Eisele, and Tim Lomax, December 2012; Western U.S. Cities, The Mobility Data for Phoenix, AZ and The Mobility Data for Tucson, AZ.

Average commute time data come from the U.S. Census Bureau, American Community Survey, Table GCT0801: Mean Travel Time to Work of Workers 16 Years and Over Who Did Not Work at Home (Minutes): State -- County / County Equivalent

Data Quality Comments: 

Travel Time Index:  A measure of congestion that focuses on each trip and each mile of travel. The ratio of travel time in the peak period to travel time in free-flow.  A value of 1.30 indicates a 20-minute free-flow trip takes 26 minutes in the peak.

Annual Delay per Commuter:  A yearly sum of all the per-trip delays for those persons who travel in the peak periods (6 to 10 a.m. and 3 to 7 p.m.). This measure illustrates the effect of the per-mile congestion as well as the length of each trip.

Excess Fuel Consumed:  Increased fuel consumption due to travel in congested conditions rather than free-flow conditions.

Congestion Cost:  Value of travel delay for 2011 (estimated at $16 per hour of person travel and $88 per hour of truck time) and excess fuel consumption (estimated using state average cost per gallon).

Note: The congestion estimates for all study years are recalculated every time the methodology is altered to provide a consistent data trend.  The estimates and methodology from this report should be used in place of any other previous measures.

Disclaimer from The 2012 Urban Mobility Report: The contents of this report reflect the views of the authors, who are responsible for the facts and the accuracy of the information presented herein. This document is disseminated under the sponsorship of the U.S. Department of Transportation University Transportation Centers Program in the interest of information exchange. The U.S. Government assumes no liability for the contents or use thereof.

iconAverage Commute Time

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Visualization Notes:

Data show the mean travel time (in minutes) to work of workers 16 years and over who did not work at home.

iconTravel Time Index

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Visualization Notes:

The travel time index is the ratio of travel time in the peak period to the travel time at free-flow conditions.  A value of 1.30 indicates a 20-minute free-flow trip takes 26 minutes in the peak. Travel time has increased in both cities over the years; the recent leveling off may be a result of the economic downturn.

iconAnnual Hours of Delay Per Peak Traveler

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Visualization Notes:

The annual delay per commuter is the yearly sum of all the per-trip delays for those persons who travel in the peak periods (6 to 10 a.m. and 3 to 7 p.m.). This measure illustrates the effect of the per-mile congestion as well as the length of each trip. Tucson once lagged behind Phoenix in annual delay, but has surpassed the larger city in this indicator; however, both cities have shown declines in the annual delay per communter since peaking in 2005.

iconAnnual Excess Fuel Consumed Per Traveler

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Visualization Notes:

Congestion results in wasted fuel, resulting in costs for individual travelers that add up to millions of lost dollars for a metropolitan area. Excess fuel consumed is defined as the increased fuel consumption due to travel in congested conditions rather than free-flow conditions. Tucson drivers consume more excess fuel than their Phoenix counterparts.  This may be be due to a lower number of alternate routes in the smaller city.


iconAnnual Cost of Congestion Per Traveler

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Visualization Notes:

Congestion cost is the value of travel time delay (in 2011 estimated at $16 per hour of person travel and $88 per hour of truck time) and and excess fuel consumption (estimated using state average cost per gallon).  This cost has decreased in recent years in both Phoenix and Tucson and leveled off during the economic downturn.

Data Source

Congestion data were collected from TTI's 2012 Urban Mobility Report (Powered by INRIX Traffic Data) by David Schrank, Bill Eisele, and Tim Lomax, December 2012; Western U.S. Cities, The Mobility Data for Phoenix, AZ and The Mobility Data for Tucson, AZ.

Average commute time data come from the U.S. Census Bureau, American Community Survey, Table GCT0801: Mean Travel Time to Work of Workers 16 Years and Over Who Did Not Work at Home (Minutes): State -- County / County Equivalent